I've forgotten a lot of things about Kingdom Hearts so dont flame me please. So heres my theory. During Kh1 sora had 3 hearts in him, when he used Riku's keyblade to release his heart to darkness, he created a nobody, Roxas and in the process created Namine. Heres how i look at it, Namine is created from both Kairi and Ven's hearts, while Roxas is created from Sora and Ven's hearts. The reason Namine isint a nobody is because both Kairi and Ven have hearts of pure light. Sora has darkness in his heart like most people, but Ven doesn't, so when they created Roxas, they created like a half nobody, explaining Roxas's ability to cry in Days. I look at Xion as being connected to Kairi and Sora's heats, so the same thing applies to her. Tell me if im wrong about anything, or if this theory has flaws, i would like to know your thoughts on this.